1. Field of the Invention
The present invention relates to multiple channel communication systems and, more particularly, to a system and method for combining a multiple number of individual transmission channels, each operating at a selectable transmission frequency that is within a correspondingly individual fixed bandwidth window, in a multiple channel communication system.
2. Description of the Prior Art
Frequency agility, or the ability to select an allocated frequency within an assigned band of frequencies, is a desirable characteristic of a multiple channel communication system. A cellular telephone communication system, in particular, benefits from frequency agility by combining a multiple number of channel transmitters, each transmitting at a selected frequency, in a multiple channel communication system. A current method of providing frequency agility in a cellular telephone communication system is realized by motor tuning each individual resonator of a channel transmitter combiner filter. The channel transmitter combiner filter resonators are motor tuned to allow a transmission frequency from an associated channel transmitter to pass. Since the transmission frequency of a channel transmitter may need to be changed, the resonators of an associated channel transmitter combiner filter must be retuned to accommodate for such a change.
Several individually and uniquely motor tuned channel transmitter combiner filters, and their associated channel transmitters, can be grouped together in a parallel connection to a common antenna. This connection permits simultaneous transmissions from several channel transmitters to be combined at a single antenna, thus a channel transmitter combiner. In such a motor tuned cellular telephone communication system, there is a complexity associated with controlling the motor tuning of the channel transmitter combiner filter resonators. This complexity is due to a series of electromechanical relays and electronic feedback circuits that are required of the motor tuning process. As a result of this complexity, the system exhibits a low reliability and a high cost.
It is therefore desirable to obtain frequency agility in cellular telephone communication systems without the complexity of motor tuned channel transmitter combiner filters.